This research program focuses on theoretical and empirical studies that address current issues in cochlear mechanics relevant to noninvasive evaluation of cochlear function. The major objectives of these studies are to understand cochlear-wave propagation and to characterize cochlear compression. These objectives are approached through six specific aims. The first three aims focus on aspects of cochlear-wave propagation through modeling efforts directed at the following theoretical issues: (1) appropriate characterization of cochlear-amplifier gain;(2) a more complete understanding of distortion-product retrograde wave propagation;and (3) understanding the mechanisms that underlie notches in basilar-membrane measurements. The next three aims characterize cochlear compression growth through a combination of empirical studies involving human subjects and theoretical work involving models of cochlear mechanics. Specifically, these three studies are designed to increase our understanding of the relation between: (4) compression growth rate (CGR) and the slope of forward-masking psychometric functions;(5) CGR and suppression growth rate;and (6) CGR and cochlear reflectance. The modeling work will facilitate interpretation of the measurements and provide a deeper understanding of cochlear wave-propagation, cochlear compression, and negative damping regions. Reliable estimation of CGR is clinically significant for the remediation of hearing loss because its deviation from normal provides a precise estimate of the amount of compression that an external hearing aid needs to provide. The goal of the proposed research is the development of a computational model of cochlear mechanics that will facilitate the interpretation of noninvasive measures of peripheral auditory status in humans. This work is relevant to public-health because people with hearing loss not only have problems hearing soft sounds, they also experience sounds growing louder too quickly. Understanding how the sense organ of hearing (the cochlea) influences the growth of loudness should provide useful information for the design of hearing aids tailored to individual needs.